Attempt #1 at cross-DB select distinct

select_distinct.rb

# So, a SELECT DISTINCT on some DBs requires that all order values are in the select clause.
# I'm hoping there's a better cross-platform way of doing this without branching, and I
# kind of think I must be overlooking something that's already built-in.
# Open to suggestions!
def distinct_relation(relation)
  offset, limit = relation.offset_value, relation.limit_value
  klass.select('DISTINCT subquery.*').
        from(Arel::Nodes::As.new(
          Arel::Nodes::Grouping.new(relation.except(:offset, :limit).arel.ast),
          Arel.sql('subquery')
        ))
        .offset(offset).limit(limit)
end